Phosphating solutions



United States Patent 3,307,979 PHOSPHATING SOLUTIONS Wesley B. Upham, Hollywood, Fla., assignor to The gilllbrizol Corporation, Wicklilfe, Ohio, a corporation of no No Drawing. Continuation of application Ser. No. 179,196, Mar. 12, 1962. This application Oct. 11, 1965, Ser. No. 494,889

6 Claims. (Cl. 148-615) This application is a continuation of co-pending U.S. application Ser. No. 179,196, filed Mar. 12, 1962, which is a continuation-in-part of co-pending US. application Ser. No. 113,092, filed May 29,1961, now U.S. 3,116,178.

This invention relates to improved aqueous phosphating solutions. In a more particular sense it relates to aqueous phosphating solutions having reduced tendency to form blush rust on ferrous metal surfaces.

It is known in the metal finishing art to provide metal surfaces, especially ferrous surfaces, with an inorganic phosphate coating by contacting them with an aqueous phosphating solution. The phosphate coating protects the metal surface to a limited extent against corrosion and serves as an excellent base for the later application of organic coatings such as paint, lacquer, varnish, primers, synthetic resins, enamel, and the like.

Such inorganic phosphate coatings are generally formed on a metal surface by means of aqueous solutions which contain the phosphate ion and, optionally, certain auxiliary ions including metallic ions such as sodium, zinc, cadmium, iron, copper, lead, nickel, cobalt, and antimony ions, and non-metallic ions such as ammonium, chloride, bromide, nitrate, and chlorate ions. These auxiliary ions modify the character of the phosphate coating and adapt it for a wide variety of applications.

The preparation and use of aqueous phosphating solutions is .well known in the metal finishing art as shown by US. Patents 1,206,075; 1,247,668; 1,305,331; 1,485,025; 1,610,362; 1,980,518; 2,001,754; and 2,859,145.

Aqueous phosphating solutions are generally prepared by dissolving in water minor amounts of phosphoric acid and, optionally, a metal salt such as a nitrate, phosphate, nitrite, sulfate, chloride, or bromide of sodium, zinc, cadmium, iron, nickel, copper, lead, or antimony. Ordinarily an oxidizing agent such as sodium chlorate, potassium perborate, sodium nitrate, ammonium nitrate, sodium chlorite, potassium perchlorate, or hydrogen peroxide is included -in the phosphating solution to depolarize the metal surface being treated and thereby increase the rate at which the phosphate coating is formed on the metal surface. Other auxiliary agents such as antisludging agents, coloring agents, and metal cleansing agents may also be incorporated in the phosphating solution. One common type of commercial phosphating bath which contains zinc ion, phosphate ion, and a depolarizer is made by dissolving small amounts of zinc dihydrogen phosphate, sodium nitrate, and phosphoric acid in water.

In order to provide the commercially satisfactory coating weights and coating speeds, an aqueous phosphating solution should generally have a total acidity within the range from about '5 to about 100 points, preferably from about to about 50 points. It is possible, however, by certain special techniques to employ phosphating solutions having a total acidity substantially higher than points, e.g., 125, 200, 250, or 300 points or more. The

term points total acidity as employed in the phosphating art represents the number of milliliters of 0.1 normal sodium hydroxide solution required to neutralize a 10 milliliter sample of a phosphating solution in the presence of phenolphthalein as an indicator.

A particularly desirable and effective class of aqueous phosphating solutions or baths is set forth in co-pending application Ser. No. 373,449, filed Aug. 10, 1953, now US. Patent 3,090,709. It is intended that the disclosure of the said application be considered as forming a part of the present specification. The phosphating solutions described therein have a total acidity within the range from about 5 to about 100 points and contain as essential ingredients zinc ion, phosphate ion, nitrate ion, and an ion selected from the group consisting of lithium, beryllium, magnesium, calcium, strontium, cadmium, and barium ions. Such phosphating solutions provide a dense, adherent, micro-crystalline or amorphous phosphate coating which shows substantially no visible crystal structure at a magnification of 100 diameters and which is preferred for the purposes of the present invention.

In view of the extensive commercial development of the phosphating art and the many journal publications and patents describing the application of phosphating solutions, it is believed unnecessary to lengthen this specification unduly by a detailed recitation of the many ways in which the phosphating step may be accomplished. Suflice it to say that any of the commonly used phosphating techniques such as spraying, brushing, dipping, roller-coating, or flow-coating may be employed, and that the temperature of the aqueous phosphating solution may vary within wide limits, e.g., from room temperature to about 212 F. In general best results are obtained when the aqueous phosphating solution is used at a temperature within the range from about to about 210 F. If desired, however, the aqueous phosphating bath may be used at higher temperatures, e.g., 225 'F., 250 F., or even 300 F., by employing superatmospheric pressures.

In the ordinary practice of phosphating a metal surface, such surface is first cleaned by physical and/or chemical means to remove any grease, dirt, or oxides and then it is phosphated in the manner described above.

The phosphating operation is usually carried out until the weight of the phosphate coating formed on the metallic surface is at least about 25 milligrams per square foot of surface area and is preferably within the range from about 100 to about 1000 milligrams per square foot of surface area. The time required to form the phosphate coating will vary according to the temperature, the type of phosphating solution employed, the particular technique of applying the phosphating solution, and the coating weight desired. In most instances, however, the time required to produce a phosphate coating of the weight preferred for the purpose of the present invention will be within the range of from about one-quarter minute to about 15 to 20 minutes.

Upon completion of the phosphating operation, the phosphated article is rinsed, optionally, with water and/ or a hot dilute aqueous solution of chromic acid cont-aining from about 0.01 to about 0.2 percent of C1-C The chromic acid rinse appears to seal the phosphate coating and improve its utility as a base for the application of paint, lacquer, varnish, and the like. In lieu of the dilute aqueous chromic acid, dilute aqueous solutions of metal chromates, metal dichromates, chromic acid-phosphoric acid mixtures, and chromic acid-metal dichromate mixtures may be used.

One problem common to all of these known phosphating solutions and phosphating techniques is their tendency to form a thin film of iron oxide or blush rust on a ferrous metal surface. The blush rust phenomenon is particularly prevalent in spray-phosphating operations where the ferrous article is surrounded by a hot, humid atmosphere containing oxygen, water vapor, and fine droplets of the phosphating solution. Under these conditions, two competing reactions occur, viz., an oxidation of the ferrous surface by the water vapor-oxygen mixture and the desired reaction of the phosphating solution with the ferrous surface. The formerreaction is believed to be responsible for the formation of blush rust.

Attempts have been made to suppress the formation of blush rust by the addition of passivating agents such as metallic nitrites and metallic dichrornates to the phosphating solution. Although these efforts have been more or less successful in reducing the incidence of blush rust, they have introduced certain new problems, principally a greater rate of sludge formation in the phosphating bath in the case of nitrites, and a reduction in coating weights and coating speeds in the case of dichromates. Under certain operating conditions, metal dichromates passivate the ferrous surface to such an extent that it Will no longer receive a phosphate coating.

It is an object of the present invention to provide improved aqueous phosphating solutions.

It is a further object to provide phosphating solutions which reduce the incidence of blush rust.

Another object is to provide a convenient and economical process for phosphating ferrous metal surfaces which reduces the formation of blush rust without adversely affecting the sludging or coating characteristics of the phosphating solution.

These and other objects are achieved by providing an aqueous phosphating solution having a total acidity within the range from about 5 to about 100 points and containing as essential ingredients zinc ion, phosphate ion, and the anion of a hydroxy-aliphatic carboxylic acid having from 3 to about 20 carbon atoms.

In its preferred embodiment, the present invention is directed to an aqueous phosphating solution having a total acidity within the range from about 5 to about 100 points and containing as essential ingredients zinc ion, preferably in an amount from about 0.1 to about 1.0 percent; phosphate ion, preferably in an amount from about 0.25 to about 2.0 percent; nitrate ion, preferably in an amount from about 0.25 to about 8.0 percent; an ion selected from the group consisting of lithium, beryllium, magnesium, calcium, strontium, cadmium, and barium ions, preferably in an amount from about 0.1 to about 4.0 percent; and from about 0.002 to about 5.0 percent of the anion of a hydroxy-aliphatic carboxylic acid having from 3 to about 20 carbon atoms.

Best results, both from the standpoint of economy, excellence of the phosphate coating, and suppression of blush rust are obtained with an aqueous phosphating solution having a total acidity within the range from about 5 to about 50 points and containing as essential ingredients from about 0.1 to about 0.6 percent of zinc ion; from about 0.3 to about 1.5 percent of phosphate ion; from about 0.5 to about 6.0 percent of nitrate ion; from about 0.1 to about 1.5 percent of calcium ion; and from about 0.005 to about 1.0 percent of the anion of a hydroxyaliphatic carboxylic acid having from 3 to about carbon atoms and containing at least one hydroxyl group alpha to a carboxylic acid group.

The anions of the hydroxyaliphatic car-boxylic acid used to suppress blush rust in the phosphating solutions of this invention may be supplied conveniently by the free acid and/or a salt thereof. Thus, for example, an addition to the phosphating solution of the free hydroxyaliphatic carboxylic acid, its ammonium salt, or its light or heavy metal salt, such as, e.g., a sodium, potassium, lithium, calcium, strontium, barium, copper, lead, or nickel salt, serves the purposes of the present invention. This is not to say that the acids and salts are of equal effectiveness. It has been found, for example, that certain salts of hydroxy-aliphatic carboxylic acids are effective at lower concentrations than are the parent acids. It is also desirable in certain instances to use mixtures of different acids, different salts, or different acids and salts.

The term hydroxyaliphatic carboxylic acid is used herein in a generic sense to represent acids conforming for the most part to the formula wherein R represents an aliphatic or cycloaliphatic residue and x and y are integers from 1 to about 8. As indicated earlier, the hydroxyaliphatic carboxylic acid will contain at least 3 carbon atoms, generally not more than about 20 carbon atoms, and preferably not more than about 10 carbon atoms. Thus, glycolic acid (i.e., hydroxyacetic acid) is not suitable for the purposes of the present invention. Especially preferred are those acids which contain at least one hydroxyl group alpha to a carboxylic acid group such as lactic acid, tartaric acid, gluconic acid, and hexahydroxyheptanoic acid.

Examples of acids which are useful per se or in the form of salts for the purposes of this invention include lactic acid, malic acid, citramalic acid, tartronic acid, methyl tartronic acid, tartaric acid, citric acid, glyceric acid, 2-methylglyceric acid, dihydroxymaleic acid, 1,2- dihydroxyglutaric acid, 1,3-dihydroxyglutaric acid, mucic acid, erythronic acid, tigliceric acid, threonic acid, digitoxic acid, malomalic acid, itamalic acid, and a wide variety of acids which are readily available from the controlled oxidation of aldose sugars, including acids such as gluconic acid, hexahydroxyheptanoic acid, mannoheptonic acid, mannonic acid, idonic acid, galactonic acid, rhamnohexonic acid, rhamnonic acid, rhamnoheptonic acid, rhamnoctonic acid, rhamnotetronic acid, glucoheptonic acid, mannooctanic acid, gluco-octonic acid, galaheptonic acid, gala-octonic acid, gluco-nononic acid, mannonononic acid, and octahydroxyarachidic acid. Substituents such as chloro, bromo, fluoro, ester, ether, sulfide, nitroso, nitro, etc., may also be present in the acid.

Because of their commercial availability, stability in storage, and low cost, the alkali metal salts and especially the sodium and/or potassium salts are preferred as a source of the anion of the hydroxyaliphatic carboxylic acid. A preference is expressed for sodium gluconate, sodium hexahydroxyheptanoate, sodium potassium tartrate (Rochelle salt), and sodium lactate. By reason of its effectiveness at very low concentrations, Rochelle salt is particularly preferred.

The hydroxyaliphatic carboxylic acid compound (i.e., the acid or salt) is generally employed in an amount sufficient to impart at least about 0.002 percent by weight and preferably from about 0.005 to about 5.0 percent of the acid anion to the phosphating solution. Amounts of such anion below about 0.002 percent appear to have little effect in reducing blush rust and amounts over 5.0 percent, although effective, contribute little added protection and are une-conomical. From the standpoint of both economy and effectiveness, amounts from about 0.005 to about 1.0 percent are particularly preferred.

Specific examples of phosphating solutions of the present invention are shown in Table I (except for the Points total acid, the values given indicate the percentages by weight of the several ions in the phosphating solution) TABLE I.PHOSPHATING SOLUTION Ion A B o D E F G H I I 0.10 0.15 0.10 0.22 =0.23 0.9' =0.1 1.0' 2.0 5.0 1.5 0.5 0.15 Points Total A010 12 12 12 30 30 30 10 11 Ton K L M N o P Q R s '1 Points 1 01514010 31 80 12 12 12 12 8 8 8 8 *Hydroxyaliphatic earboxylic acid anion. 1 Gluconie acid anion.

2 Hexahydroxyheptanoie acid anion.

' Rhamnohexonic acid anion.

I Rhamnonic acid anion.

The preparation of certain of the above phosphating solutions is carried out as follows:

SOLUTION A 4.98 g. of Zn(NO 6.88 g. of NaH PO 6.32 g. of Ca(NO -3H O, and 2.5 g. of sodium gluconate are dissolved in suflicient water to make one liter of solution.

SOLUTION B This solution is prepared in the same manner as Solution A, except that 2.5 g. of sodium hexahydroxyheptanoate is used in lieu of the sodium gluconate.

SOLUTION C A mixture of 1.95 ml. of 42 Baum HNO and 4.66 ml. of commercial 75% H PO is neutralized With 1.92 g. of ZnO and 1.46 ml. of 50% aqueous NaOH. Then 20 g. of Ca(NO -3H O and 10 g. of sodium hexahydroxyheptanoate are added and the Whole is diluted with sufficient water to make one liter of solution.

SOLUTION D SOLUTION M 100 ml. of water, 6.8 g. of 75% H PO 3.8 g. of 42 Baum HNO 1.9 g. of ZnO, and 1.2 g. of CaO are 5 Gluco-octonlc acid anion. 6 Gala-octonic acid anion. Glueonononic acid anion. lLaetic acid anion. ",Tartaric acid anion.

3 g. of sodium hexahydroxyheptanoate are then dissolved in this solution.

SOLUTION N ml. of Water, 7.4 g. of 75% H PO 2.7 g. of 42 Baum HNO 1.9 g. of ZnO, and 2.2 g. of 50% aqueous NaOH are thoroughly mixed and then diluted with Water to make one liter of solution. 20 g. of Ca(NO -3H O and 1 g. of sodium lactate are then dissolved in this solution.

SOLUTION O This solution is prepared in the same manner set forth for Solution N, except that 0.5 g. of Rochelle salt is used in lieu of the sodium lactate.

SOLUTION P This solution is prepared in the same manner set forth for Solution N, except that 1 g. of lactic acid is used in lieu of the sodium lactate.

SOLUTION Q 100 ml. of Water, 4.2 g. of 75% H PO 2.2 g. of 42 Baum HNO 1.5 g. of ZnO, and 1.8 g. of 50% aqueous NaOH are thoroughly mixed and then diluted with water to make one liter of solution. 12 g. of Ca(NO -3H O and 0.5 g. of sodium hexahydroxyheptanoate are then dissolved in this solution.

SOLUTION R This solution is prepared in the same manner set forth for Solution Q, except that 0.05 g. of Rochelle salt is used in lieu of the sodium hexahydroxyheptanoate.

SOLUTION s This solution is prepared in the same manner set forth for Solution Q, except that 0.35 g. of tartaric acid is used in lieu of the sodium hexahydroxyheptanoate.

7 SOLUTION T This solution is prepared in the same manner set forth for Solution Q, except that 0.35 g. of sodium acid tartrate is used in lieu of the sodium hexahydroxyheptanoate.

The following examples are submitted to set forth specific modes of applying the invention. They are intended for purposes of illustration only and are not to be construed as limiting the scope of the invention, except as the latter is defined by the appended claims.

Example 1 Soluition A and 3 similar phosphating solutions containing larger or smaller quantities of so-dium gluconate than Solution A were prepared. A control solution similar to Solution A but not containing sodium gluconate was also prepared.

Each solution was heated to 200 F. and used to phosphate a 3-inch square test panel of clean, solvent-degreased ZO-gauge cold-rolled steel. A test panel was immersed in each solution for seconds, suspended in the vapor above the hot solution for one minute and then removed to a rack and allowed to dry.

An inspection of the test panels for blush rust yielded the following data:

Percent gluconic acid anion in the phosphating solution: Blush rust formation None (control) Heavy.

0.22 (Solution A) Very light.

0.44 None.

Example 2 A series of experiments like those carried out in Example 1 were conducted using phosphating Solution B, two solutions similar to Solution B but containing larger quantities of sodium hexahydroxyheptanoate, and a control solution similar to Solution B but not containing sodium hexahydroxyheptanoate. The results obtained were as follows:

Percent hexahydroxyheptanoic acid anion in the phospating solution: Blush rust formation None (control) Heavy.

0.23 (Solution B) Very light.

0.45 None.

Example 3 Solution C, 4 similar phosphating solutions containing smaller quantities of sodium hexahydroxyheptanoate, and a control solution similar to Solution C but not containing sodium hexahydroxyheptanoate were employed for the spray-phosphating of 4-inchx 8-inch ZO-gauge coldrolled steel test panels.

The overall phosphating operation was carried out as follows: Each of six solvent-degreased, 4-inchx 8-inch test panels was bent 180 degrees along its 4-inch dimension on a conical mandrel. Each of the formed panels was sprayed for 1 minute at 170-180 F. with an aqueous solution containing 2 ounces/ gal. of a commercial alkaline cleanser, sprayed for 3 minutes at 120 F. with tap water, and then sprayed with the selected phosphatin g solution for 2 minutes at 160165 F. While each formed panel was still wet with phosphating solution, it was sprayrinsed successively with cold tap water for 1 minute and warm (90 F.), dilute aqueous chromic acid (0.125 g. CrO /liter) for 1 minute.

After the panels had dried, they were inspected for blush rust formation on the convex and the concave surfaces:

Blush rust formation on- Percent hexahydroxyheptanoic acid anion in the phosphating solution Concave Convex surface surface None (control) Heavy None 0.23 Modcrate Do.

o Do. Light Do. o Do. None Do.

Example 4 A full-scale evaluation of the effectiveness of a phosphating solution of this invention was conducted in a plant where steel bodies for pickup trucks were spray-phosphated prior to painting. The use of a phosphating solution similar to Solution C but not containing sodium hexahydroxyheptanoate had resulted in the formation-of blush rust on certain portions of the bodies, principally the tail-light, front-panel, under-fender, under-cab, and spare tire well areas.

The use of a phosphating solution similar to Solution C but containing 0.3 percent sodium hexahydroxyheptanoate substantially reduced the incidence of blush rust. Visual inspections of a large number of cabs which had been phosphated with this solution yielded the following data (made with reference to results obtained with the phosphating solution which did not contain sodium hexahydroxyheptanoate) Area inspected: Inspectors remarks Tail-light Complete elimination of blush rust. Front-panel elimination of blush rust. Under-fender 25% elimination of blush rust. Under-cab 50% elimination of blush rust. Spare tire well- 90% elimination of blush rust.

Example 5 Solution M and two similar solutions, one devoid of sodium hexahydroxyheptanoate and the other containing twice as much sodium hexahydroxyheptanoate as S0- lution M, were prepared.

Each of three 4-inch x 4-inch panels of cold-rolled 20- gauge SAE 1020 steel was placed in contact with a steel cone of fixed size and shape and then bent along a 4-inch dimension. The bent panels were cleaned by immersion for 2 minutes at 200 F. in an aqueous cleanser consisting of water plus 40 g./liter of a commercial, alkali-base cleanser. Thereafter, the three panels were immersed, respectively, in the three above-described phosphating solutions for 30 seconds at 175 F., suspended in the vapor above the phosphating solution for 2 minutes, rinsed with a dilute aqueous solution of chromic acid (0.5 g. of CrO /liter), and rinsed with acetone to dry.

The panels were inspected and given a blush rust rating on a scale of 0 to 100, '0 representing a blush rustfree panel and 100 representing a panel completely covered with blush rust. The results were as follows:

Percent hexahydroxyheptanoic acid anion Blush rust in the phosphating solution: rating None (control) 100 0.27 (Solution M) 10 0.54 0

Example 6 Solution N and three similar solutions, one devoid of sodium lactate and the other two containing, respectively, three times and six times as much sodium lactate as Solution N, were prepared.

In a manner like that described in Example 5, these phosphating solutions were tested to determine their ability to lessen or to prevent the development of blush rust on bent steel panels. The results were as follows:

Percent lactic acid anion Blush rust in the phosphating solution: rating None (control) 100 0.078 (Solution N) 30 0.234 i 0.468 0 Example 7 Solution 0 and three similar solutions, one devoid of Rochelle salt (sodium potassium tartrate tetrahydrate) and the other two containing, respectively, twice and four times as much Rochelle salt as Solution 0, were prepared.

In a manner like that described in Example 5, these phosphating solutions were tested to determine their ability to lessen or to prevent the development of blush rust on bent steel panels. The results were as follows:

Percent tartaric acid anion Blush rust in the phosphating solution: rating None (control) 100 0.038 (Solution 0) 0.076 l0 0.152 10 It will be noted that the tartaric acid anion (from Rochelle salt) was effective in substantially reducing blush rust at a concentration (0.038 percent) lower than that of any hydroxyaliphatic carboxylic acid anion investigated in Examples 1-6, inclusive.

Example 8 Solution P and two similar solutions, one devoid of lactic acid and the other containing six times as much lactic acid as Solution P, were prepared.

In a manner like that set forth in Example 5, these phosphating solutions were tested to determine their ability to lessen or to prevent the development of blush rust on bent steel panels. The test results were as follows: Percent lactic acid anion Blush rust in the phosphating solution: rating None (control) 100 0.097 (Solution P) 90 0.582 10 By reference to 'Example 6, it will be noted that lactic acid is somewhat less effective than sodium lactate in reducing the formation of blush rust.

Example 9 Solution Q and two similar solutions, one devoid of sodium hexahydroxyheptanoate and the other containing three times as much sodium hexahydroxyheptanoate as Solution Q, were prepared.

Nine clean, solvent-degreased, 4-inch x 8-inch panels of 24-gauge cold-rolled steel were bent along their 4-inch dimension in the manner described in Example 5.

Three sets of three panels each were phosphated, respectively, in a continuous spray-line apparatus according to the three schedules given below:

Aqueous alkaline cleanser spray (1.5 oz./ gal. of a commercial alkali-base cleanser) for 40 seconds at 175 180 F.

Water spray for 3 minutes at 110 F.

Solution Q spray for 1.75 minutes at 160165 F.

Water spray for 40 seconds at 120 F.

Aqueous chromic acid spray (1/ 8 g. CrO /liter) for 40 seconds at 90 F.

Like schedule (a), but using in lieu of Solution Q a similar solution devoid of sodium hexahydroxyheptanoate.

10 Like schedule (a), but using in lieu of Solution Q a similar solution containing three times as much sodium hexahydroxyheptanoate.

After all three sets of panels had been phosphated, they were examined to determine the percent reduction in blush rust due to the presence of the hexahydroxyheptanoic acid anion. The results were as follows:

Percent reduction in blush rust (aver- Percent hexahydroxyheptanoic acid anion in the phosphating solution: age of three panels) {None 0.045 (Solution Q) 25 0.135 1 Control.

Example 10 in blush rust (average of three panels) Percent tartaric acid anion (from Rochelle salt) in the phosphating solution:

None (1) 0.0039 (Solution R) 50 0.0195 75 1 Control.

It will be noted that Rochelle salt was more effective than either the tartaric acid of Example 11 or the sodium acid tartrate of Example 12 in reducing blush rust.

Example 11 Solution S and two similar solutions, one devoid of tartaric acid and the other containing about twice as much tartaric acid as Solution S, were prepared.

In a manner like that described in Example 9, three sets of three bent steel panels each were spray-phosphated, respectively, with the above-noted phosphating solutions. An examination of the panels yielded the following data:

Percent reduction in blush rust (average of three panels) Percent tartaric acid anion from tartaric acid) in the phosphating solution:

None 0.035 25 0.075 50 Control.

Example 12 Percent reduction in blush rust (average of three panels) Percent tartaric acid anion (from sodium acid tartrate) in the phosphating solution:

None

0030 (Solution T) 50 0.060 50 Control.

What is claimed is:

-1. An aqueous phosphating solution having a total acidity within the range from about 5 to points wherein the active ingredients consist essentially of Zinc ion, phosphate ion, nitrate ion, an ion selected from the group consisting of lithium, beryllium, magnesium, calcium, strontium, cadmium, and barium ions, and from about 0.002 to about 5.0% of the anion of a hydroxy-aliphatic carboxyl ic acid having 3 to about 20 carbon atoms, said anion having not more than two hydroxy groups if it contains five or more carbon atoms.

2. An aqueous phosphating solution according to claim 1 containing from about 0.01 to about 1.0% of zinc ion, from about 0.25 to about 2.0% of phosphate ion, from about 0.25 to about 8.0% of nitrate ion, and from about 0.1 to 4.0% of lithium, beryllium, magnesium, calcium, strontium, cadmium, or barium ion.

3. An aqueous phosphatin-g solution having a total acidity within the range from about 5 to about 50 points and containing as essential ingredients from about 0.1 to about 0.6 percent of zinc ion, from about 0.3 to about 1.5 percent of phosphate ion, from about 0.5 to about 6.0 percent of nitrate ion, from about 0.1 to about 1.5 percent of calcium ion, and from about 0.005 to about 1.0 percent of the anion of a hydroxyaliphatic carboxylic acid having from 3 to about 10 carbon atoms and containing at least one hydroxyl group alpha to a carboxylic acid group, said anion having not more than two hydroxy groups if it contains five or more carbon atoms.

4. An aqueous phosphating solution in accordance with claim 3 wherein the anion of the hydroXy-aliphatic carboxylic acid is the anion of lactic acid.

5. An aqueous phosphating solution in accordance with claim 3 wherein the anion of the hydroxyaliphatic carboxylic acid is the anion of tartaric acid.

6. An aqueous phosphating solution in accordance with claim 5 wherein the anion of tartaric acid is supplied by sodium potassium tartrate.

References Cited by the Examiner UNITED STATES PATENTS 2,331,196 10/1943 Jernstedt et a1. 1486.l5 2,516,139 7/1950 Mazia l486.15 2,692,189 10/1954 Ro 1486.15 X 2,826,517 3/1958 Miller 1486.15 3,090,709 5/1963 Hendricks 148--6.15 3,116,178 12/1963 Upham 148-615 FOREIGN PATENTS 983,924 2/1965 Great Britain.

ALFRED L. LEAVITT, Primary Examiner. RALPH S. KENDALL, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,307,979 March 7, 1967 Wesley B. Upham It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Columns 5 and 6, TABLE I, under column B, line 4 thereof, for "9.71" read 0.71 column 10, line 49, for "from tartaric acid)" read (from tartaric acid) Signed and sealed this 12th day of November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. AN AQUEOUS PHOSPHATING SOLUTION HAVING A TOTAL ACIDITY WITHIN THE RANGE FROM ABOUT 5 TO 100 POINTS WHEREIN THE ACTIVE INGREDIENTS CONSIST ESSENTIALLY OF ZINC ION, PHOSPHATE ION, NITRATE ION, AND ION SELECTED FROM THE GROUP CONSISTING OF LITHIUM, BERYLIUM, MAGNESIUM, CALCIUM, STRONTIUM, CADMIUM, AND BARIUM IONS, AND FROM ABOUT 0.002 TO ABOUT 5.0% OF THE ANION OF A HYDROXY-ALIPHATIC CARBOXYLIC ACID HAVING 3 TO ABOUT 20 CARBON ATOMS, SAID ANION HAVING NOT MORE THAN TWO HYDROXY GROUPS IF IT CONTAINS FIVE OR MORE CARBON ATOMS. 